Entities with substantial printing demands typically use a production printer. A production printer is a high-speed printer used for volume printing (e.g., one hundred pages per minute or more). Production printers include continuous-forms printers that print on a web of print media stored on a large roll.
A production printer typically includes a localized print controller that controls the overall operation of the printing system, and a print engine (sometimes referred to as an “imaging engine” or a “marking engine”). The print engine includes one or more printhead assemblies, with each assembly including a printhead controller and a printhead (or array of printheads). An individual printhead includes multiple (e.g., hundreds of) tiny nozzles that are operable to discharge ink as controlled by the printhead controller. A printhead array is formed from multiple printheads that are spaced in series across the width of the web of print media.
While printing, the web is quickly passed underneath the nozzles, which discharge ink at intervals to form pixels on the web. In order to ensure that the web is consistently positioned underneath the nozzles, steering systems can be used to align the web laterally with respect to its direction of travel. For example, these steering systems can be calibrated when the printer is first installed. However, even when the web is aligned, fluctuations in the physical properties of the web itself (e.g., small micron-level variations along the edge of the web, lateral tension variation along the web, orientation of the fibers in the web, etc.) can cause the web to experience lateral shifts during printing. This means that printed output for a print job can appear to shift back and forth across the pages of a document. Even though the individual shifts can be small (e.g., on the order of microns), the shifts can reduce print quality. For example, when multiple printheads are used by a printer to form a mixed color pixel, a small fluctuation in web position can cause an upstream printhead to mark the correct physical location, while a downstream printhead marks the wrong physical location. This distorts the final color of the pixel in the printed job.